• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.39-48
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• 2014

Variable valve actuation system is one of the widely used techniques to improve the fuel efficiency and power of automotive engines. 2-step variable valve actuation systems are also paid attention for the application to direct acting type valve train systems. Besides its advantages in size, weight, relatively simple structure, ets, however, 2-step variable valve actuation system has inherent disadvantages in dynamic instability of switching system to alter discontinuous lift modes. In this study, both experimental and analytical studies are performed to understand the dynamic behavior of a switching mechanism of a 2-step variable valve actuation system, and present a design method to improve its dynamic instability.

• Journal of Chest Surgery
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• v.11 no.4
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• pp.428-432
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• 1978

Between Jan. and Oct. 1978, mitral valve Replacement had been performed on eight patients using porcine aortic valve mounted on flexible polypropylene or Egyloil wire and Dacron covered stent. Mitral valve replacement was performed on five, mitral valve replacement with tricuspid valve replacement on two, and mitral valve replacement with tricuspid valve annuloplasty on 1 patient using five Carpentier and five Hancock Xenograft. Overall operative deaths were 2 cases. All other 6 cases did well after surgery and improved. No systemic thromboembolism occurred without anticoagulant-No valve failure took place. The results are satisfactory.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.238-244
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• 2002

A 5-valve(intake 3-valve) engine has been developed to increase engine performance. These engines have a high power caused by the decrease of inertia mass of an intake valve and the increase of intake effective area. In this study, in-cylinder flow patterns were visualized with laser sheet method and velocity profiles at near intake valves were inspected by using a two-color PIV. In addition, steady flow tests were performed to quantify tumble ratio of flow-fields generated by a tumble control valve(TCV). Experimental results of steady flow test show that the cure of tumble ratio in intake 3-valve engine farmed as a S shape with valve lift changes. This tendency is different from the one in intake 2-valve engine. Using laser sheet method and two color PIV method, we can find that the intake flow through upper valve increases and the velocity gradient also slightly increases as valve lift increases. From this study, the in-cylinder flow characteristics around intake valves were made clearly.

• Journal of Chest Surgery
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• v.27 no.10
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• pp.838-845
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• 1994

From April, 1982 to December, 1992, multiple valve replacement was performed in 100 patients. Mitral and aortic valve replacement were done in 86 patients, 9 underwent mitral and tricuspid valve replacement, 4 patients underwent triple valve replacement and 1 patient underwent aortic and tricuspid valve replacement. Of the valve implanted, 100 were St. Jude, 64 Duromedics, 19 Carpentier-Edwards, 13 Bj rk-Shiley, 6 Ionescu-Shiley, and 2 Medronics.The hospital mortality rate was 15%[15 patients] and the late mortality rate was 7%[7 patients], the mortality rate was high in early operative period but decreased with time[20% at 1986, 18.2% at 1987, 9.5% at 1988, 11.1% at 1989, 12.5% at 1990, 11.8% at 1991, 0% at 1992]. The causes of death were low cardiac output in 8, sudden death in 3, CHF in 3, bleeding in 2, cerebral thromboembolism in 1, leukemia in 1, multiorgan failure in 1 and so on. The actuarial survival rate excluding operative death was 73% at 10 years.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.166-174
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• 1999

The flow characteristics of 2-valve and 4-valve cylinder heads with various blocked-valve were experimentally investigated in a steady flow rig. Effects of the blocked-valve configurations on flow coefficient, swirl and tumble intensity are studied. Compared to the conventional valve, the blocked valve in both cylinder heads have the much lower flow coefficient and the much higher intensity of swirl and tumble. Under the same size of blockage, the value of flow coefficient and swirl(or tumble) intensity were varied according to the position of blockage. Throughout these steady flow test the optimized positions of blockage in both cylinder heads were determined.

• Journal of Chest Surgery
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• v.26 no.3
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• pp.191-195
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• 1993

Among 25 consecutive cases having undergone mitral valve surgery between March 1991 and June 1992 in Gill General Hospital, 11 patients[44%] who had undergone mitral valve reconstruction using prosthetic rings is evaluated and presented. Patients` mean age is 43 + 19 years[range:16-72], and they are consisted with 4 males and 7 females. Mitral valve insufficiency is due to degenerative disease in 6 cases[55%] and rheumatic disease in 5 patients[45%]. Carpentier`s functional classification I is 2 cases, II is 6 cases, and III is 2 cases. Surgical techniques include prosthetic ring annuloplasty[11 patients, 100%], chorda shortening[6, 55%], leaflet mobilization[4,36%], new chorda formation[2, 18%], chorda transposition[1, 9%] commissurotomy[3, 27%], and papillary muscle splitting[3, 27%]. Average number of mitral anatomic lesions per patient are 2.7 and we used average 2.8 procedures upon mitral valve apparatus per patient. There were no surgical mortality and no late valve related admission during the mean follow up period of 17 months. The mean functional class[NYHA] is 2.81 preoperatively and improved to 1.10 postoperatively. Doppler echocardiography showed much improvement from grade II MR [1 case], grade III MR [1 case] and 9 cases of grade IV MR to 6 cases of patients showed no MR, only trace MR in 4 cases, and grade I MR was found only in one patient with NYHA functional class II postoperatively. The postoperative mean mitral valve area is $2.10+0.28cm^2$. We conclude that mitral reconstruction is a predictable and stable operation.

• Journal of the Korean Ceramic Society
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• v.35 no.2
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• pp.172-179
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• 1998

Valve lifter namely tappet is supported by lifter hole which is located upper side of camshaft in cylinder block transforms rotatic mvement of camshaft into linear movement and helps to open and shut the en-gine valve as an engine parts. The face of valve lifter which is continuously contacting with camshaft brings about abnormal wears such as unfair wear and early wear because it is severely loaded in the valve train system. These wears act as a defect like over-clearance and cause imperfect combustion of fuel during the valve lifting in the combustion chamber. Consequently this imperfect combustion makes the engine out-put decrease and has cause on air pollution. To prevent these wears therefore The valve lifter cast in me-tal developed into SiC ceramics valve lifter which has an excellence in wear and impact resistance As a results the optimum process conditions like injection condition mixture ratio and debonding process could be established. After sintering fine-sinered dual microstructure in which prior ${\alpha}$-SiC matches well with new SiC(${\beta}$-SiC) produced by reaction among the ${\alpha}$-SiC carbon and silicon was obtained. Based on the study it is verified that mechanical properties of SiC valve lifter are excellent in Vickers hardness 1100-1200 bending strength (300-350 Pa) fracture toughness(1.5-1.7 Mpa$.$m1/2) Through engine dynamo test-ing SiC valve lifter and metal valve lifter are examined and compared into abnormal phenomena such as early fracture unfair and early wear. It is hoped that this research will serve as an important springboard for the future study of heavy duty diesel engine parts developed by ceramics which has a good wear resis-tance relaibility and lightability.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.128-134
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• 2013

A 2-way solenoid valve regulates to maintain the pressure of ullage volume of propellant tanks when the command is given by control system for the liquid-propellant feeding system of space launch vehicle. The simulation model of solenoid valve for pressurization is designed with AMESim to verify the designs and evaluate the dynamic characteristics and pneumatic behaviors of valve. To improve the accuracy of the model, numerical flow analysis by using FLUNET code. The simulation results of their operating durations of valve by AMESim analysis are matched up with the results of experiments and validate valve model. Using the model, we analyze performance of valve; opening/closing pressure, operating time on various design factors of basic valve and control valve; geometrical size of valve seat, ratio of basic valve and sealing area.

• The KSFM Journal of Fluid Machinery
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• v.2 no.4 s.5
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• pp.24-30
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• 1999

An analytical study has been carried out to investigate the effects of the check valve installation on the volumetric and adiabatic efficiencies in a scroll compressor. Both the valve displacement limit and the valve stiffness affected the valve motion, the pressure upstream of the valve, and the pattern of the mass flow through the valve to the discharge plenum. Nonetheless, the presence of the check valve did not cause any noticeable change in the volumetric efficiency. Only a slight increase in the compression work was needed to overcome the pressure increase in front of the valve. The pressure build-up upstream of the valve can be alleviated with the larger limit of the valve lift and a smaller valve stiffness.

• Journal of Chest Surgery
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• v.17 no.2
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• pp.223-230
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• 1984

Since January 1977 to the end of September 1982, total 60 Ionescu-Shiley pericardial xenograft heart valves were implanted for valve replacement in 50 patients at the Han Yang University Hospital. The operative procedures were as follow: Mitral valve replacement [MVR] in 25 patients, Mitral valve replacement [MVR] and Tricuspid valve [TV] annuloplasty in 7 patients, Aortic valve replacement [AVR] in 8 patients, Aortic valve replacement [AVR] and Mitral valve replacement [MVR] in 8 patients. Aortic valve replacement [AVR] and Mitral valve replacement [MVR] and Tricuspid valve [TV] annuloplasty in 2 patients. To evaluate the immediate hemodynamic changes after valve replacements, the pressures of each cardiac chamber and ulmonary artery were checked before and after valve replacement on the operation table. Right ventricle [RV] pressure was decreased from 52.09\ulcorner6.71 to 45.57\ulcorner5.03 mmHg, Pulmonary artery [PA] pressure was decreased from 45.97\ulcorner2.69 to 41.00\ulcorner3.99 mmHg, and Left atrium [LA] pressure was decreased from 30.33\ulcorner13.02 to 22.76\ulcorner.97 mmHg before and after valve replacement. In MVR group, RV pressure was decreased from 49.17\ulcorner7.89 to 43.14\ulcorner4.14 mmHg, PA pressure was decreased from 44.67\ulcorner3.18 to 38.67\ulcorner2.85 mmHg, and LA pressure was decreased from 31.46\ulcorner13.47 to 21.91\ulcorner.17 mmHg. In AVR group, RV pressure was decreased from 53.0\ulcorner7.44 to 44.71 \ulcorner3.24 mmHg, PA pressure was decreased from 34.83\ulcorner0.73 to 31.86\ulcorner.36 mmHg, and LA pressure was not changed. In double valve replacement [MVR and AVR] group, RV pressure was decreased from 57.50\ulcorner3.82 to 42.50\ulcorner.80 mmHg, PA pressure was decreased from 51.17\ulcorner1.42 to 43.33\ulcorner4.53mmHig, and LA pressure was decreased from 34.33\ulcorner2.09 to 25.50\ulcorner0.21 mmHg. But in the group where MVR and TV annuloplasty were performed, preoperative RV and PA pressure were markedly increased and no pressure decrease in RV and PA noticed after valve replacement. This study shows good immediate postoperative hemodynamic results after valve replacement using Ionescu-Shiley xenograft valve except in the cases of MVR and TV annuloplasty and advanced disease with pulmonary hypertension.